1. Field of the Invention
This invention relates to focal plane arrays and, more specifically, to a slot shield for a focal plane array and method of fabricating the slot shield.
2. Brief Description of the Prior Art
When detecting incident energy transmitted from a remote source and primarily infrared energy, it is often desirable that the remote source not be aware that the energy it is transmitting is being detected. A problem in this regard is that focal plane arrays (FPAs), a principal devices used to receive incident energy and primarily infrared energy, tend to reflect the received energy along the incident energy path. It follows that the reflected energy can often be detected by the original transmitter whereby the original transmitter becomes aware that someone is detecting the energy being transmitted. In order to minimize the possibility that the transmitter will be aware that detection is taking place, it is necessary that the energy received by the detector either be absorbed, be reflected along a path other than the incident path or a combination thereof.
To minimize reflection along the incident path, focal plane arrays generally are provided with a slot shield on the surface thereof. Slot shields are generally a layer of reflective material, disposed on the surface of the FPA with a slot therein over the detector region to permit IR to pass through the slot to the detector. The purpose of the slot shield is to prevent or at least minimize reflection of incident energy impinging upon the detector along its incident path so that reflected energy cannot be picked up by the original transmitter thereof along its incident path. The shield portion of the slot shield which defines the slot is formed from a specular, absorptive material, generally doped silicon. The slot shield operates on the theory that most of the energy impinging upon the detector is travelling at an acute or obtuse angle relative thereto and that such energy will therefore be reflected along a path other than the incident path.
In accordance with the prior art fabrication procedures for slot shields, the slot shield was fabricated from thin layers of silicon, then secured with an epoxy and aligned on a previously fabricated infrared focal plane array. Problems encountered with prior art infrared focal plane array slot shields are poor suitability to mass production in that a great deal of labor is involved in their fabrication, low fabrication yield, possible device damage during mount and alignment and restricted placement tolerance due to alignment capability. It is therefore apparent that an improved procedure for fabrication of slot shields for focal plane arrays is highly desirable.